1. Field of Invention
This invention relates generally to gas sensors and methods of analyzing gases.
2. Related Art
Methods such as the Fischer-Tropsch process that produce synthetic liquid fuels from carbon monoxide and hydrogen mixtures require strict control of process parameters to efficiently produce the desired grades of fuel products. One of the most critical of these parameters is the ratio of hydrogen to carbon monoxide.
The majority of synthetic fuel production methods involve partial oxidation or steam reforming processes. These processes are usually performed at high pressure (about 500 psi) and high temperature (about 800° C.). Many of the analyzers for monitoring and control of the H2/CO ratio utilize sensors that operate at ambient temperature and pressure. As a result, cooling and pressure reduction devices must be installed between the process and the CO and H2 analyzers. These devices add considerable complexity to the overall process and make the analyzer response times relatively slow. In addition, the analysis of H2 and CO is often performed separately rather than by a single analyzer providing both gas measurements simultaneously.
Many current methods of CO analysis typically require the presence of oxygen to operate. In U.S. Pat. No. 4,073,698 to Blurton et al., a method is described based on the selective oxidation of hydrogen, which prevents this gas from interfering with the measurement of CO. In U.S. Pat. No. 4,394,239 to Kitzelmann et al., a method is described for measuring the concentration of CO and H2 in ambient air. Another method, described in U.S. Pat. No. 4,397,888 to Yannopoulos et al., requires oxygen across a stannic oxide thick-film sensor that uses different dopants to distinguish between CO and H2. A method described in U.S. Pat. No. 5,439,580 to Akbar et al. also requires gas-specific dopants to distinguish between CO and H2.
The measurement of CO and H2 in a process gas stream is a particular example of a gas measurement that could be carried out faster and more efficiently at elevated temperatures and pressures. There remains a need for continued development of devices and methods for high temperature and high pressure gas analysis.